1. Field of the Invention
The present invention relates to a coating system based on a copolymer with valuable surface qualities. More particularly, the present invention relates to urethane-siloxane copolymers, and to coating compositions, to methods of making and using those compositions, and to articles coated with those compositions to impart the surface qualities of low friction, abrasion resistance, moisture resistance, and ice release properties.
2. Description of Background and Relevant Materials
Coatings may be used to alter the surface characteristics of substances whose desireable qualities do not extend to their native surface properties, or whose native surface properties are simply inappropriate to their operating environment.
For example, elastic or resilient materials may possess shock-absorbing and sound deadening qualities which render them extremely useful in a wide range of applications. However, they are also characterized by high surface friction, which is also referred to as low surface slip, and generally have poor resistance to surface abrasion. Porous rubbers, which are lightweight in addition to being shock-absorbing and sound-deadening, may have low surface slip and be even more susceptible to surface wear than nonporous rubbers.
In order to overcome these problems, it would be desireable to develop a coating that adheres well to substances such as rubber or plastic, and thereby provides them with a high slip, low-friction outer layer which is also abrasion-resistant. It would be particularly advantageous if such a coating had the additional quality of repelling moisture.
While high slip, abrasion-resistant coatings are not new, a one-pack coating that intrinsically provides these qualities, adheres to substrates such as rubber and plastic, and possesses the further qualities of water repellency and ice release without any need for additives, does not appear in the prior art.
Japanese Patent 0130880 is directed to compositions that contain urethane resin paint and silicone resin. When mixed just prior to use and coated onto cement, these compositions are asserted to repel moisture and prevent frost damage.
Japanese Patent 0062575 is directed to mixtures of silicone oil with thermo-setting or wet-setting polyurethane, diluted with a solvent such as toluene. These mixtures may be used as surface-treating agents, such as by spray-coating weather stripping.
Japanese Patent 046008 is directed to forming a prepolymer by reacting silicone polymer with isocyanate. The prepolymer is then mixed with polyurethane resin, and the resulting mixture may be used as a surface treating agent for car door weather stripping.
EVANS et al., U.S. Pat. No. 2,893,898, is directed to making textile materials water-repellent by treating them with a blend of an isocyanate and an organosilicone compound. The material to be treated may be contacted with the isocyanate and the organosilicone in either order or simultaneously, generally followed by heating.
SHORR, U.S. Pat. No. 2,924,587, is directed to a method for making textile fabrics water repellent by treating them with a blend of a siloxane and a polyisocyanate, in an inert solvent. SHORR speculates that the isocyanate cures the silicone and chemically bonds it to the surface of the textile fabric being treated.
REISCHL et al., U.S. Pat. No. 3,243,475, is directed to production of polyurethanes with improved moisture resistance. A polyester is reacted with a polyisocyanate in a reaction mixture containing an organo silicon compound, which has a reactive hydrogen linked to a silicon atom through an alkylene radical. The resulting polyurethanes may be used to make films, coatings, adhesives, foams, automobile tires, shoe soles, upholstery, and similar products.
HALUSKA, U.S. Pat. No. 3,246,048, is directed to organosiloxane-polyether-polyurethane copolymers with improved resistance to moisture. A siloxane, a hydroxylated polyether, and an organic isocyanate are combined in a spontaneous, exothermic reaction to yield the copolymer, which may used in applications such as shock mounts and rubber tires. These products are stated to exhibit superior moisture resistance compared to products that do not contain the silicone component.
NYILAS, U.S. Pat. No. 3,562,352, is directed to block copolymers of a polyurethane and a polysiloxane having direct silicon-nitrogen linkages. The copolymers are stated to have medical applications because they have high blood compatability and are non-thrombogenic, possibly due to an absence of hydrogen binding sites.
HISAKI et al., U.S. Pat. No. 4,464,431, is directed to reducing the coefficient of friction of sportswear fabric by treating the fabric with an aqueous mixture that includes an organopolysiloxane and a urethane prepolymer. The free isocyanate group of the urethane prepolymer, which is initially blocked, is freed by heating, which causes the organopolysiloxane to become bound to the fabric being treated over a layer of polyurethane.
MABUCHI et al., U.S. Pat. No. 4,572,871, is directed to a glass-run for the window glass of an automobile composed of a blend of a first urethane prepolymer; a castor oil polyol; a second urethane prepolymer; a fluoro resin; and a silicone oil. This blend is asserted to exhibit high abrasion-resistance.
YAMAZAKI et al., U.S. Pat. No. 4,572,872, is directed to a glass-run for the window glass of an automobile having improved abrasion resistance. The glass run is formed from a composition that includes a urethane polymer; a castor oil polyol; a urethane prepolymer; a fluoro carbon resin; a silicone oil; and at least one of a silica, a clay, and calcium carbonate.
It is noteworthy, when viewing the present invention in light of the the prior art, that most of the foregoing patents do not appear to employ any copolymerization of the various silicon-containing ingredients mentioned therein with urethane or isocyate. For example, while silicone oil is mentioned as an additive in several of these patents, there is no indication that the oil reacts chemically with other ingredients in the blend at issue.
Copolymerization in some form does take place in Japanese Patent 046008; REISCHL; HALUSKA; and NYLLAS. However, REISCHL and HALUSKA are directed towards improving the moisture resistance of polyurethanes, while NYLLAS is directed towards providing blood contact surfaces for devices having medical applications. The Japanese patent deals with weatherstripping for car doors and is directed towards a silicone-isocyanate prepolymer mixed with polyurethane resin, rather than towards a urethane-siloxane copolymer. None of these references teaches a urethane-siloxane copolymer disclosed to be useful in providing high-slip, low-friction coatings which are resistant to abrasion and which adhere to substrates such as rubbers and plastics.
As can be readily seen from the preceding discussion, nowhere in this prior art is there described a one-pack coating system capable of imparting high surface slip, abrasion resistance, and water resistance when coated onto a rubber or plastic substrate. The MABUCHI et al. and YAMAZAKI et al. patents, which represent the only prior art located in one particularly preferred field of the present invention, employ cumbersome, multi-component systems. Moreover, these systems are not asserted to provide high surface slip or to be water resistant, both of these properties being critical to applications such as automotive window channels.
The window glass in a car window will typically be opened and closed thousands of times over the life of the car. It is essential that the material lining the channels in which the glass moves have exceptionally high surface slip and resistance to abrasion, to last for the life of the car.
Moreover, the lining material should be moisture resistant to form a watertight seal with the window glass and thereby prevent water both from entering the interior of the car, and from seeping down into the interior of the door and causing body damage and/or rusting of the door opening and locking mechanisms.
The need for the liner to have high surface slip is not simply a corollary of minimizing surface wear, but is equally importantly as a user consideration. The resistance to raising and lowering a window to be expected from any significant adherence between the liner and the window glass, such as might be expected with uncoated rubber, would not only be a serious source of aggravation to the user, but would place a serious strain on the components of the mechanism for moving the window, shortening their life expectancy.
As a final consideration, it would be valuable if the liner had very low adherence to ice, that is, possessed ice release properties. The familiar phenomenon of car windows being frozen in place by wet snow followed by low temperatures, or by an ice storm, is not only annoying but potentially dangerous due to consequent obstruction of the driver's vision. Moreover, even if the user is willing to take the trouble to chip the ice or frozen snow loose after it fails to dislodge easily, any appreciable degree of adherence between the frozen material and the liner may result in damage to the liner resulting from the force used to separate the two.